JP2019173172A - Magnesium oxide for annealing separation agent, and manufacturing method of directional electromagnetic steel sheet - Google Patents

Abstract

To provide a magnesium oxide for annealing separation agent for providing a directional electromagnetic steel sheet excellent in magnetic property.SOLUTION: There is provided magnesium oxide for annealing separation agent containing boron of 400 to 1500 mass.ppm, sodium of 1 to 650 mass.ppm, chlorine of 500 mass.ppm or less, sulfur in terms of SOof 0.10 to 0.70 mass%, and having a molar ratio of boron, sodium, chlorine, and sulfur (Cl+S)/(B+Na) of 0.50 to 0.80, and a directional electromagnetic steel sheet is manufactured by using the same.SELECTED DRAWING: None

Description

  The present invention relates to magnesium oxide for an annealing separator and a method for producing a grain-oriented electrical steel sheet using the same.

Oriented electrical steel sheets used for transformers and generators are generally hot-rolled silicon steel containing about 3% silicon (Si), then cold-rolled to the final thickness, and then decarburized and annealed. It is manufactured by finish annealing. In decarburization annealing (primary recrystallization annealing), a silicon dioxide film is formed on the surface of the steel sheet, a slurry containing magnesium oxide for annealing separator is applied to the surface, dried, wound into a coil, and then annealed to the finish. By doing so, as shown in the following reaction formula, silicon dioxide (SiO ₂ ) and magnesium oxide (MgO) react to form a forsterite (Mg ₂ SiO ₄ ) coating on the steel sheet surface.
2MgO + SiO ₂ → Mg ₂ SiO ₄ (I)
This forsterite film is important because it imparts tension to the surface of the steel sheet, reduces iron loss, improves magnetic properties, and provides insulation to the steel sheet.

On the other hand, when looking at the base metal part under the forsterite film, the applied annealing separator affects the formation and growth behavior of precipitates and the growth behavior of crystal grains. The product characteristics of electrical steel sheets vary greatly. For example, if too much moisture is brought into the slurry when MgO is slurried, the steel sheet is oxidized and the magnetic properties are deteriorated or point defects are generated in the coating. It is also known that impurities contained in MgO penetrate into steel during annealing, and the secondary recrystallization behavior changes through changes in the grain growth inhibition force. In order to improve the above, various studies have been conducted on trace components contained in magnesium oxide for annealing separators as described below. As trace components for which the control of the content in magnesium oxide for annealing separators is studied, calcium oxide (CaO), boron (B), sulfurous acid (SO ₃ ), fluorine (F), chlorine (Cl), etc. Can be mentioned. Furthermore, not only the content of a trace component but also an attempt to examine the structure of a compound containing a trace component element in magnesium oxide for annealing separator.

Therefore, first, among the trace components for which the control of the content in the magnesium oxide for the annealing separator is being studied, when manufacturing magnesium oxide, attention is paid to CaO remaining as an impurity. The relationship is set to a specific value ([CaO%] × [B%] = 0.025 to 0.30), CAA value (citric acid activity value) (60 to 250 seconds), particle size (10 μm or less: 60% or more) ), An annealing separator having excellent adhesion to the steel sheet and excellent reactivity with the undercoat is proposed (Patent Document 1). Considering the process of obtaining MgO from the slurry of MgCl ₂ and Ca (OH) ₂ via Mg (OH) ₂ , not only CaO as an impurity but also the amount of halogen is limited to 0.35. ~ 0.5 An annealing separator containing 0 wt%, SO ₃ 0.3 to 1.5 wt%, halogen 0.05 wt% or less and B 0.06 to 0.10 wt% has been proposed (Patent Document 2).

In particular, as a focus on chlorine, a chlorine compound selected from Mg, Ca, Ba, Cu, Fe, Zn, Mn, Zr, Co, Ni, Al, Sn, and V in the raw material adjustment stage in the manufacturing process. 1 or 2 or more, and 0.005 to 0.060% as Cl, and B is [Cl (%)] × [B (%)] = 0.001 to 0.004, respectively. Uniform high-tensile glass coating and excellent magnetic properties, characterized by being contained and having a CAA value of 50 to 150 seconds at a measurement temperature of 30 ° C. and a particle size of 10 μm or less being 70% or more An annealing separator for grain-oriented electrical steel sheets is proposed (Patent Document 3), which is also a magnesia slurry maintained at 25 ° C. or lower for coating cold-rolled grain-oriented silicon steel before finish high temperature annealing. A A) magnesia with a major amount of magnesia particles having a citric acid activity of 200 seconds or less; b) with at least 0.01% by weight of chlorine from a metal chloride selected from the group consisting of Mg, Ca, Na and / or K Total chlorine level in magnesia from 0.01 to 0.20% by weight, based on the weight of magnesia, c) up to 15% TiO ₂ ; d) up to 10% SiO ₂ ; e) up to 15% Cr And c) a magnesia slurry characterized by being substantially composed of boron up to 0.3% (Patent Document 4), and finally the hydration moisture of the annealing separator mainly composed of MgO is set to 0. 5 to 2.0%, added to the annealing separator so that the total chlorine content of the chlorine compound is 0.020% to 0.080%, and the hydration moisture and Cl content of the annealing separator Relational expressions have been proposed ( Patent Document 5).

Furthermore, focusing on not only chlorine and CaO but also boron (B) and sulfurous acid (SO ₃ ) in the manufacturing process, and controlling CAA and the amount of hydration, as the magnesia in the annealing separator, the Cl concentration of impurities There 0.01~0.04mass%, CaO concentration 0.25~0.70mass%, B concentration 0.05~0.15mass%, SO ₃ concentration 0.05~0.50mass%, is CAA40% 50 to 90 seconds were satisfied, and the hydration amount in a hydration test at 20 ° C. for 30 minutes was 1.5 to 2.5 mass%, and the hydration amount in a hydration test at 20 ° C. for 180 minutes was 3.0. Using powder having a mass of ˜5.0 mass% (Patent Document 6), as magnesia, the BET specific surface area is 36 to 50 m ² / g, the Cl concentration of impurities is 0.02 to 0.04%, and the CAA 40% is 35 ~ 65 seconds, C What A80% is 80 to 160 seconds, blended least 10 mass%, and the average properties of magnesia consisting of a mixture of two or more kinds, BET specific surface area: 20-35 meters ² / g, impurities Cl concentration: 0. from 01 to .04%, CaO concentration: 0.25 to 0.70%, B concentration: 0.05~0.15%, SO ₃ concentration: 0.05~0.50%, CAA40%: 55~85 Second, CAA 80%: 100-250 seconds and 20 ° C., 60 minutes of hydration amount: 1.5-3.5 mass%, magnesia for annealing separator is proposed (Patent Document 7).

On the other hand, a sodium phosphate compound is used as an additive for magnesium oxide (Patent Document 8), and ammonium chloride (NH ₄ Cl or NH ₄ ) is used as a nitride-based and / or sulfide-based inhibitor for magnesium oxide. Cl · nH ₂ O), which prevents early deterioration in the temperature raising process for final annealing (Patent Document 9), a water-soluble compound is added to an annealing separator containing magnesia as a main component, and a secondary inhibitor The thing which solves the problem in the raw material which contains is proposed (patent document 10).

Japanese Patent Publication No. 4-25349 Japanese Patent No. 3043975 Japanese Patent No. 2690841 Japanese Patent No. 2686455 Japanese Patent No. 4823719 Japanese Patent No. 4893259 Japanese Patent No. 5245277 Japanese Patent No. 3730254 Japanese Patent No. 4194653 Japanese Patent No. 4192822

  As described above, various researches and developments have been made on improving the magnetic properties of grain-oriented electrical steel sheets. However, conventional magnesium oxide for annealing separators cannot sufficiently improve the magnetic properties of grain-oriented electrical steel sheets. That is, magnesium oxide for annealing separators having sufficient performance has not been found yet.

  Therefore, an object of the present invention is to provide magnesium oxide for an annealing separator for obtaining a grain-oriented electrical steel sheet having excellent magnetic properties. Specifically, magnesium oxide for an annealing separator capable of forming an excellent forsterite film and providing a grain-oriented electrical steel sheet having excellent iron loss and magnetic flux density characteristics, and a grain-oriented electrical steel sheet using the same. An object is to provide a manufacturing method.

  As a result of diligent research in consideration of the above-described prior art, the present inventors considered the total mole number of the boron component and sodium component involved in the composition of the forsterite film, the chlorine component involved in the formation rate of the forsterite film, and An excellent forsterite film can be formed by limiting the total number of moles of chlorine and sulfur with respect to the total number of moles of boron and sodium in the annealing separator while limiting the sulfur component, and a grain-oriented electrical steel sheet. It has been found that the iron loss and magnetic flux density characteristics can be improved.

That is, the present invention contains 400 to 1500 ppm by mass of boron, 1 to 650 ppm by mass of sodium, 500 ppm by mass or less of chlorine, 0.10 to 0.70% by mass of sulfur in terms of SO ₃ , and boron and Provided is a magnesium oxide for an annealing separator having a total content molar ratio of chlorine and sulfur (Cl + S) / (B + Na) of 0.50 to 0.80 with respect to the total content of sodium.

  According to the present invention, in the annealing separator having magnesium oxide as the main component, considering the total number of moles of the boron component and the sodium component, while limiting the chlorine component and the sulfur component, the inclusion of boron and sodium in the annealing separator When the total number of moles of chlorine and sulfur relative to the total number of moles is limited to a predetermined ratio, a grain-oriented electrical steel sheet having excellent magnetic properties can be obtained. Specifically, by using the magnesium oxide for annealing separator according to the present invention, after forming a silicon dioxide film on the surface of the steel sheet, by applying the annealing separator on the surface of the silicon dioxide film and annealing, An excellent forsterite film can be formed on the surface, and the iron loss and magnetic flux density characteristics of the grain-oriented electrical steel sheet can be improved.

  By containing 100 to 1000 ppm by mass of phosphorus, a further excellent forsterite film can be formed, and the iron loss and magnetic flux density characteristics of the grain-oriented electrical steel sheet can be further improved.

The magnesium oxide of the present invention is mainly composed of magnesium oxide, boron is 400 to 1500 mass ppm, sodium is 1 to 650 mass ppm, chlorine is 500 mass ppm or less, and sulfur is 0.10 to 0.70 mass in terms of SO _3. %, And the total molar ratio of chlorine and sulfur to the total moles of boron and sodium (Cl + S) / (B + Na) is 0.50 to 0.80, containing 100 to 1000 ppm by mass of phosphorus, direction Used as an annealing separator for heat-resistant electrical steel sheets. As for the physical properties, for example, the volume-based cumulative 10% particle diameter (D ₁₀ ) is 3 μm or less, and for example, CAA 40% is 50 to 200 seconds. In the present specification, unless otherwise specified, ppm means mass ppm, and% means mass%.

  First, the content of each component contained in the magnesium oxide of the present invention as an additive component will be described in order.

Boron (B) is an element that promotes film formation of forsterite Mg ₂ SiO ₄ formed by the reaction between the annealing separator MgO and the surface SiO _{2 of the} electrical steel sheet. Usually, in the manufacturing process of the annealing separator MgO A predetermined amount may be added, for example, at least one selected from boric acid, magnesium borate, calcium borate, sodium borate, and boron oxide, magnesium chloride solution or water that is a raw material of magnesium hydroxide before the reaction It can be added to the calcium oxide slurry, and can be added to the magnesium hydroxide slurry after the reaction. Further, it can be mixed and added to the magnesium hydroxide powder after filtration, washing and drying. Thereafter, magnesium hydroxide is baked to obtain a magnesium oxide powder, and boron in the magnesium oxide is adjusted to 400 to 1500 ppm. The amount of boron in magnesium oxide can be further adjusted by mixing magnesium oxides having different boron contents obtained by the same production method. Here, if it is less than 400 ppm, a sufficient film of forsterite cannot be formed. On the other hand, if it exceeds 1500 ppm, an excessively thick film is formed, causing point-like defects, and none of the good film characteristics can be obtained. Therefore, the range is 400-1500 ppm, preferably 550-1400 ppm, more preferably 700-1300 ppm.

  Sodium (Na) is an element that adjusts the forsterite film formation rate, and usually a predetermined amount may be added in the manufacturing process of the annealing separator MgO. For example, sodium chloride, sodium nitrate, sodium phosphate, sodium sulfate, And at least one selected from sodium borate can be added to the magnesium hydroxide solution or calcium hydroxide slurry, which is the raw material of magnesium hydroxide before the reaction, and added to the magnesium hydroxide slurry after the reaction. can do. Further, it can be mixed and added to the magnesium hydroxide powder after filtration, washing and drying. Thereafter, magnesium hydroxide is calcined to obtain a magnesium oxide powder, and sodium in the magnesium oxide is adjusted to 1 to 650 ppm. Sodium in magnesium oxide can be further adjusted by mixing magnesium oxides having different sodium contents obtained by the same production method. Here, if it is less than 1 ppm, the forsterite film formation rate is slow and a sufficient film is not formed, while if it exceeds 650 ppm, the film formation rate is too high, and an excessively thick film is formed, causing point defects. In either case, good film properties cannot be obtained. Therefore, the range is 1 to 650 ppm, preferably 5 to 640 ppm, more preferably 10 to 630 ppm, and particularly preferably 10 to 620 ppm.

Chlorine (Cl) is an element that promotes forsterite film formation, and the addition of chloride lowers the glass film formation temperature and seals the surface at a low temperature. Usually, the amount of chlorine can be controlled by the reaction conditions (reaction temperature, reaction time, reaction rate) in the process of producing Mg (OH) ₂ from a slurry of MgCl ₂ and Ca (OH) ₂ , but the amount of chlorine is insufficient In this case, the metal chloride can be added to the magnesium chloride solution or calcium hydroxide slurry, which is the raw material of the magnesium hydroxide before the reaction, and added to the magnesium hydroxide slurry after the reaction. Can do. Further, it can be mixed and added to the magnesium hydroxide powder after filtration, washing and drying. Although it will not specifically limit if it is a composition containing chlorine as said metal chloride, For example, it can control by adding at least 1 or more types selected from sodium chloride, magnesium chloride, and calcium chloride. Moreover, the particle shape, particle diameter, and aggregation state of magnesium hydroxide can be controlled by reaction conditions, and the chlorine amount can be controlled by washing conditions (time, amount of water at the time of washing, etc.). Chlorine in magnesium oxide can be further adjusted by mixing magnesium oxides having different chlorine contents obtained by the same production method. Here, if it exceeds 500 ppm, film formation is excessively promoted, an excessively thick film is formed, causing point defects, and good film characteristics cannot be obtained. The chlorine content in the magnesium oxide finally obtained by firing is 500 ppm or less, preferably in the range of 50 to 450 ppm, more preferably in the range of 150 to 400 ppm.

Sulfur (S) is an element that promotes forsterite film formation and affects the form of the film. Usually, a predetermined amount may be added in the manufacturing process of the annealing separator MgO. For example, at least one selected from magnesium sulfate, calcium sulfate, and sodium sulfate may be a magnesium chloride solution that is a raw material of magnesium hydroxide before the reaction or It can be added to the calcium hydroxide slurry and can be added to the magnesium hydroxide slurry after the reaction. Further, it can be mixed and added to the magnesium hydroxide powder after filtration, washing and drying. Thereafter, magnesium hydroxide is fired to obtain a magnesium oxide powder, and the sulfur in the magnesium oxide is adjusted to be 0.10 to 0.70% by mass in terms of SO ₃ . The sulfur in the magnesium oxide can be further adjusted by mixing magnesium oxides having different sulfur contents obtained by the same production method. Here, if the amount is less than 0.10% by mass, the unevenness at the interface between the base iron and the film is lost, and the film is easily peeled off. Characteristics are not obtained. Accordingly, the range is 0.10 to 0.70 mass%, preferably 0.20 to 0.60 mass%, more preferably 0.30 to 0.50 mass%.

  Chlorine and sulfur are elements that promote film formation, while boron is also an element that promotes film formation. However, while chlorine and sulfur contribute to the reactivity of the surface hydration layer of MgO and promote coating, boron is baked due to the presence of glassy boron compounds on the surface of MgO particles. As a factor that contributes to film formation, excess of chlorine and sulfur directly affects defects due to overoxidation of the film, but excess of boron is not so much. Therefore, it is important to first consider the balance of the film-promoting elements by the ratio of the mole of boron to the total moles of chlorine and sulfur (Cl + S) / B. On the other hand, although sodium is a film-inhibiting element, it easily binds to other metal ions to form a low-melting compound, and when the film-promoting element is excessive, an excessive film that becomes an anchor in the depth direction is formed. Adversely affects the magnetic flux density. Therefore, it is important for sodium to balance adhesion and high magnetic flux density by balancing the total content of chlorine and sulfur with respect to the boron containing glassy boron compound on the surface of MgO particles. It is. Therefore, it is preferable that the total molar content ratio of chlorine and sulfur (Cl + S) / (B + Na) with respect to the boron and sodium-containing mole is adjusted in the range of 0.50 to 0.80 and the formation of the forsterite film is favorably maintained.

  Phosphorus (P) is an element that promotes film formation. Usually, a predetermined amount may be added in the manufacturing process of the annealing separator MgO, for example, a magnesium chloride solution that is a raw material of magnesium hydroxide before reaction with at least one kind selected from phosphoric acid, magnesium phosphate, and calcium phosphate or It can be added to the calcium hydroxide slurry, can be added to the magnesium hydroxide slurry after the reaction, and can be mixed and added to the magnesium hydroxide powder after filtration, washing with water and drying. Thereafter, magnesium hydroxide is fired to obtain a magnesium oxide powder, and the phosphorus in the magnesium oxide is adjusted to 100 to 1000 ppm. The phosphorus in the magnesium oxide can be further adjusted by mixing magnesium oxides having different phosphorus contents obtained by the same production method. That is, if it is less than 100 ppm, a sufficient film is not formed. On the other hand, if it exceeds 1000 ppm, an excessively thick film is formed, causing point defects, and none of the film characteristics are good. Therefore, the range is 100 to 1000 ppm, preferably 120 to 900 ppm, more preferably 150 to 600 ppm.

  Phosphorus, like sulfur and chlorine, contributes to the reactivity of the MgO surface hydrated layer, and as a result, promotes coating. The phosphorus in the magnesium oxide is adjusted to 100 to 1000 ppm, but the total molar ratio of chlorine and sulfur to the boron and sodium-containing moles (S + Cl) / (B + Na) includes the number of moles containing phosphorus, (S + Cl + P) / (B + Na) is preferably in the range of 0.55 to 0.85, more preferably in the range of 0.60 to 0.80.

The volume-based cumulative 10% particle diameter (D ₁₀ ) is preferably 3 μm or less, and the citric acid activity (CAA 40%) is preferably 50 to 200 seconds. When the volume-based cumulative 10% particle diameter (D ₁₀ ) exceeds 3 μm, the primary particle diameter of magnesium oxide becomes coarse, and the reactivity of the magnesium oxide particles becomes poor. The film is not formed, and the iron loss and magnetic flux density characteristics of the grain-oriented electrical steel sheet are deteriorated. Therefore, the range is preferably 3 μm or less, more preferably 2.9 μm or less.

  On the other hand, CAA empirically simulates the reactivity of solid phase-solid phase reaction between silicon dioxide and magnesium oxide that occurs on the surface of an actual electrical steel sheet by solid phase-liquid phase reaction. The reactivity of the magnesium oxide particle contained is measured. If CAA 40% of magnesium oxide is greater than 200 seconds, the reactivity of magnesium oxide particles is poor and the forsterite film formation rate is slow, so that a sufficient film is not formed, and the iron loss and magnetic flux density of the grain-oriented electrical steel sheet The characteristics of become worse. On the other hand, if the CAA 40% of magnesium oxide is less than 50 seconds, the reactivity of the magnesium oxide particles becomes too fast, a uniform forsterite film cannot be formed, and the iron loss and magnetic flux density characteristics of the grain-oriented electrical steel sheet deteriorate. . That is, when the above-mentioned citric acid activity is less than 50 seconds, the amount of hydration becomes too large, while when it exceeds 200 seconds, the reactivity is too low, and in any case, good film properties cannot be obtained. Accordingly, the range is preferably 50 to 200 seconds, more preferably 60 to 150 seconds. Here, citric acid activity (CAA 40%) is the temperature up to the final reaction when 40% of the final reaction equivalent of magnesium oxide is administered and stirred in a 0.4N citric acid aqueous solution at a temperature of 303K. It means time, that is, the time until citric acid is consumed and the solution becomes neutral.

  In the present invention, a known method can be used as a method for producing magnesium oxide. For example, magnesium chloride is used as a raw material, and calcium hydroxide is added to this aqueous solution in a slurry state and reacted to form magnesium hydroxide. Next, this magnesium hydroxide can be filtered, washed with water, dried and then fired in a heating furnace to form magnesium oxide, which can be pulverized to a desired particle size.

  Further, instead of calcium hydroxide, an alkaline compound having a hydroxyl group such as sodium hydroxide or potassium hydroxide can be used. Also, magnesium oxide containing aqueous solution such as seawater, irrigation, bitter juice, etc. is introduced into the reactor, and magnesium oxide is generated by the Aman process in which magnesium oxide and hydrochloric acid are directly generated at 1773 to 2273K. It can grind | pulverize to the particle size of this, and can manufacture a magnesium oxide.

  Furthermore, magnesium oxide obtained by firing mineral magnesite can be hydrated, and the resulting magnesium hydroxide can be fired and pulverized to a desired particle size to produce magnesium oxide.

  The amount of the trace content in MgO can be controlled by a known method. As a method for controlling the amount of the trace content in MgO, for example, during the manufacturing process of the crude product, or the obtained crude product so that the amount of the trace content in MgO falls within a predetermined range. Can be carried out by controlling the amount of the trace amount before the final firing. The control during the production process of the crude product is, for example, analyzed by analyzing the amount of the trace amount contained in the raw material, and based on the result, wet or dry so that the amount of the trace amount to be controlled becomes a predetermined amount. It can be controlled by adding in or removing by wet. The addition of the trace amount can be performed, for example, by mixing the elements to be added and drying. Moreover, the removal of the trace content can be performed by, for example, physically washing excess chemical content or chemically separating it. Chemical separation can be achieved by, for example, forming a soluble hydrate, dissolving, filtering, washing and separating, or forming an insoluble compound, precipitating, adsorbing and separating the precipitate. This can be done. Control of the amount of trace elements contained in the crude product before the final firing can be achieved, for example, by mixing and mixing crude products having different compositions so that the amount of trace elements can be controlled so that the amount of trace elements falls within a predetermined range. It can be controlled by adjusting the shortage and final firing. Furthermore, in order to control the amount of trace elements, in each case, after producing the crude product MgO and analyzing the resulting MgO, the above procedure is followed according to the individual results regarding the amount of trace elements Can be repeated and combined.

Magnesium oxide D ₁₀ and CAA can be adjusted by a known method, for example, by the following method. That is, by adjusting the concentration of the reaction temperature and the alkali source in the manufacturing process of the magnesium hydroxide to control the primary particle diameter and secondary particle diameter of magnesium hydroxide, adjusting the D ₁₀ and the CAA of magnesium oxide Can do. Also, by controlling the sintering temperature and time of magnesium hydroxide having a controlled particle diameter, it is possible to adjust the D ₁₀ and the CAA of magnesium oxide. _Further, as a method for adjusting the _{D 10} and CAA, measured _{D 10} and CAA after grinding, it can also be adjusted by performing a plurality of times firing. In addition, calcined magnesium oxide, jaw crusher, gyratory crusher, cone crusher, impact crusher, roll crusher, cutter mill, stamp mill, ring mill, roller mill, jet mill, hammer mill, pin mill, rotary mill, vibration mill, The CAA of magnesium oxide can also be adjusted by pulverization using a pulverizer such as a planetary mill or a ball mill. _Further, as a method for adjusting the _{D 10} and CAA, _D were measured ₁₀ and CAA after grinding, can also be adjusted by performing a plurality of times grinding.

The grain-oriented electrical steel sheet of the present invention can be manufactured, for example, by the following method. The grain-oriented electrical steel sheet hot-rolls a silicon steel slab containing Si 2.5 to 4.5%, and after pickling, performs cold rolling or performs cold rolling twice with intermediate annealing, Adjust to a predetermined plate thickness. Next, the cold-rolled coil is subjected to recrystallization annealing also serving as decarburization in a wet hydrogen atmosphere of 923 to 1173K, and at this time, an oxide film mainly composed of silica (SiO ₂ ) is formed on the steel plate surface. . The MgO for annealing separator of the present invention is uniformly dispersed in water to obtain a water slurry, and the water slurry is continuously applied onto the steel plate by roll coating or spraying and dried at about 573K. The steel plate coil thus treated is subjected to, for example, final finishing annealing at 1473K for 20 hours to form a forsterite film (Mg ₂ SiO ₄ ) on the steel plate surface. The forsterite film is an insulating film, and can impart tension to the steel sheet surface to improve the iron loss value of the grain-oriented electrical steel sheet.

  The following examples illustrate the invention in detail but are not intended to limit the invention in any way.

<Measurement method / Test method>
(1) Method for Measuring Content of Boron (B) After completely dissolving the measurement sample in hydrochloric acid, it is diluted with ultrapure water and using an ICP emission spectrometer (PS3520 VDD, manufactured by Hitachi High-Tech Science Co., Ltd.). The content of boron (B) in the sample was measured.

(2) Method for measuring content of sodium (Na) After completely dissolving the measurement sample in nitric acid, the sample was diluted with ultrapure water, and Hitachi Polarized Zeeman atomic absorption photometer (Z-2300, manufactured by Hitachi High-Technologies Corporation). Was used to measure the content of sodium (Na) in the sample.

(3) Measurement method of chlorine (Cl) content After dissolving a measurement sample in nitric acid, it is diluted with ultrapure water, and the mass is measured using a spectrophotometer (manufactured by Shimadzu UV-2550). The chlorine (Cl) concentration in the sample was calculated.

(4) Method for measuring phosphorus (P) content After dissolving the measurement sample in a mixed acid of hydrochloric acid and sulfuric acid, dilute with ultrapure water, and use an ICP emission spectroscopic analyzer (PS3520 VDD, manufactured by Hitachi High-Tech Science Corporation). Used to measure the phosphorus (P) content in the sample.

(5) Method for measuring the content of sulfur oxide (SO ₃ ) A measurement sample was molded under pressure using an aluminum ring 35 mmφ at a total pressure of 30 MPa, and a fluorescent X-ray analyzer (simultix12 type, manufactured by Rigaku Corporation) Was used to measure the content of sulfur oxide (SO ₃ ) in the sample. From this measurement result, the number of moles of sulfur (S) was calculated.

(6) and CAA40% measurement methods citric acid solution 1 × ¹⁰ -4 ^{m 3} of 0.4 N, and a 1% phenolphthalein solution in an appropriate amount as an indicator ^{(2 × 10 -6 m 3)} , 2 × 10 - Put in a ⁴ m ³ beaker, adjust the liquid temperature to 303 K, and stir at 700 rpm using a magnetic stirrer, and add 40% of the final reaction equivalent of magnesium oxide into the citric acid solution until the final reaction. , That is, the time until citric acid is consumed and the solution becomes neutral.

(7) Volume-based cumulative 10% particle size (D ₁₀ )
The measurement sample was dissolved in methanol, and the volume-based cumulative 10% particle size (D ₁₀ ) of the sample was measured using a laser diffraction / scattering particle size distribution analyzer (manufactured by MT3300EX-II LEEDS & NORTHUP). At that time, dispersion was performed for 180 seconds with ultrasonic waves of 40 W output.

(8) Measuring method of iron loss value and magnetic flux density As a test sample test steel, a silicon steel slab for a grain-oriented electrical steel sheet is hot-rolled and cold-rolled by a known method to obtain a final thickness of 0. The steel plate was 28 × 10 ⁻³ m, and further decarburized and annealed in a humid atmosphere of 25% nitrogen + 75% hydrogen. The composition of the steel sheet before decarburization annealing is mass%, C: 0.01%, Si: 3.29%, Mn: 0.09%, Al: 0.03%, S: 0.07%, N : 0.0053%, the balance being inevitable impurities and Fe. The test target magnesium oxide is made into a slurry and applied to a steel plate so that the mass after drying is 14 × 10 ⁻³ kg · m ^−2. After drying, final finishing annealing is performed at 1473 K for 20.0 hours. It was. After the final finish annealing was completed, the steel sheet was cooled, washed with water, acid washed with an aqueous hydrochloric acid solution, washed again with water and dried to form a forsterite film on the steel sheet. This steel plate was processed into a size of 20 mm × 80 mm, and the iron loss and magnetic flux density of the steel plate were measured using a magnetic property evaluation device (AC magnetization property test device SK-200, manufactured by Metron Giken Co., Ltd.). Here, the iron loss is an iron loss at a magnetic flux density of 1.7 T and a frequency of 50 Hz, and the magnetic flux density is a magnetic flux density in a magnetic field of 800 A / m.

<Examples 1-2 and Comparative Examples 1-2>
The magnesium oxide of Examples 1-2 and Comparative Examples 1-2 was obtained using the reagent. Specifically, first, magnesium chloride (reagent special grade) was dissolved in pure water to prepare a 0.5 × 10 ³ mol · m ⁻³ magnesium chloride aqueous solution. Next, calcium hydroxide (special reagent grade) was put in pure water to prepare a 0.5 × 10 ³ mol · m ⁻³ calcium hydroxide dispersion. These magnesium chloride aqueous solution and calcium hydroxide dispersion were mixed so that the molar ratio of MgCl ₂ / Ca (OH) ₂ = 1.1 was 1.0 × 10 ⁻³ m ³ to obtain a mixed solution. Thereafter, boric acid (special grade), magnesium sulfate (special grade), sodium chloride (special grade), and magnesium phosphate (primary grade) are put in an appropriate amount, and the mixture is stirred at 600 rpm using a four-blade stirring blade. The mixture was reacted at 313K for 5.5 hours to obtain a magnesium hydroxide slurry. Thereafter, the magnesium hydroxide slurry was filtered, and the obtained magnesium hydroxide was washed with 100 times the mass of pure water and dried at 378 K for 12.0 hours to obtain a magnesium hydroxide powder. After mixing an appropriate amount of magnesium chloride hexahydrate (special grade) to the obtained magnesium hydroxide powder, it was baked in an electric furnace and contains the components shown in Table 1 and Examples 1-2 and Comparative Examples 1-2. Magnesium oxide powder was obtained. The firing was performed under the condition that the CAA 40% of magnesium oxide was in the range of 80 to 100 seconds.

  About the obtained magnesium oxide powder of Examples 1-2 and Comparative Examples 1-2, as above-mentioned, a content component is measured and the iron loss and magnetic flux density of the grain-oriented electrical steel sheet obtained using these magnesium oxide powders Was measured. The results are shown in Table 1.

  As apparent from Table 1, the magnesium oxides of Examples 1 and 2 in which (Cl + S) / (B + Na) is in the range of 0.50 to 0.80 and the respective component contents are in the predetermined range are as follows. The steel sheet on which the forsterite film was formed using this magnesium oxide had excellent iron loss of 1.10 W / kg or less and magnetic flux density of 1.90 T or more. On the other hand, for the magnesium oxide of Comparative Example 1 in which (Cl + S) / (B + Na) is not in the range of 0.50 to 0.80, the iron loss of the steel sheet in which the forsterite film is formed using this magnesium oxide is large, The magnetic flux density was low. Further, even when (Cl + S) / (B + Na) is in the range of 0.50 to 0.80, the forsterite is also used for the magnesium oxide of Comparative Example 2 having a low boron and sulfur content. The iron loss of the steel sheet on which the film was formed was large, and the magnetic flux density was low.

<Examples 3-7 and Comparative Examples 3-5>
Using bitter juice, magnesium oxides of Examples 3 to 7 and Comparative Examples 3 to 5 were obtained. Specifically, first, calcium hydroxide slurry is added to bitter juice containing magnesium ions at a concentration of 2.0 × 10 ³ mol · m ⁻³ , and the magnesium hydroxide concentration after reaction is 2.0 × 10 ³ mol · m. ^-3 was added to obtain a mixed solution. Thereafter, boric acid (special grade), magnesium sulfate (special grade), sodium chloride (special grade), and magnesium phosphate (primary grade) were added in appropriate amounts and reacted at 323 K for 7.0 hours while stirring at 600 rpm. Then, it filtered with the filter press, washed with water, and dried and obtained magnesium hydroxide. An appropriate amount of magnesium chloride hexahydrate (special grade) was mixed with this magnesium hydroxide, followed by firing in a rotary kiln and pulverization to obtain magnesium oxide powders of Examples 3 to 7 and Comparative Examples 3 to 5. The firing was performed under the condition that the CAA 40% of magnesium oxide was in the range of 80 to 100 seconds.

  About the obtained magnesium oxide powder of Examples 3-7 and Comparative Examples 3-5, a content component is measured as mentioned above, and the iron loss and magnetic flux density of the grain-oriented electrical steel sheet obtained using these magnesium oxide powders Was measured. The results are shown in Table 2.

  As is apparent from Table 2, the magnesium oxides of Examples 3 to 7 in which (Cl + S) / (B + Na) is in the range of 0.50 to 0.80 and each component content is in the predetermined range are The steel sheet on which the forsterite film was formed using this magnesium oxide had excellent iron loss of 1.10 W / kg or less and magnetic flux density of 1.90 T or more. On the other hand, for the magnesium oxide of Comparative Examples 3 to 5 where (Cl + S) / (B + Na) is not in the range of 0.50 to 0.80, the steel plate in which the forsterite film was formed using the magnesium oxide of Comparative Example 3 was used. The iron loss was large and the magnetic flux density was low, and the iron loss of the steel sheet in which the forsterite film was formed using the magnesium oxides of Comparative Examples 4 and 5 was large.

  From the above, it became clear that the grain-oriented electrical steel sheet having excellent magnetic properties can be produced by using the magnesium oxide for annealing separator of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the magnesium oxide for annealing separation agents which can form the outstanding forsterite film and can provide the grain-oriented electrical steel sheet excellent in the characteristic of an iron loss and magnetic flux density can be provided.

Claims (6)

Boron is 400-1500 mass ppm, sodium is 1-650 mass ppm, chlorine is 500 mass ppm or less, sulfur is 0.10-0.70 mass% in terms of SO ₃ , and boron, sodium, chlorine, and sulfur are contained. Magnesium oxide for an annealing separator having a molar ratio (Cl + S) / (B + Na) of 0.50 to 0.80.   The magnesium oxide for annealing separators according to claim 1, wherein CAA 40% is 50 to 200 seconds. Cumulative 10% particle diameter (D ₁₀₎ is 3μm or less on a volume basis, magnesium oxide for an annealing separating agent according to claim 1 or claim 2.   Magnesium oxide for annealing separators according to any one of claims 1 to 3, containing 100 to 1000 ppm by mass of phosphorus.   An annealing separator containing magnesium oxide for an annealing separator according to any one of claims 1 to 4. Forming a silicon dioxide film on the steel sheet surface;
A method for producing a grain-oriented electrical steel sheet, comprising: applying a annealing separator according to claim 5 to a surface of a silicon dioxide film and forming a forsterite film on the surface of the steel sheet by annealing.